In Reply We appreciate the discussion by Sugiyama of potential mechanism(s) by which height gain contributes to bone acquisition as described in our study.1 Sugiyama raises several important points that deserve additional discussion.
First, he posits that a relatively low degree of mineralization, caused by high bone remodeling during growth, supports rapid increases in whole-body and skeletal site–specific BMC. This occurs because in the setting of decreased bone stiffness, there is increased bone strain and thus enhancement of mechanical strain-related stimuli, eg, as produced by physical activity and increasing height. We agree that physical activity benefits the pediatric skeleton; it is positively associated with bone z scores2 as well as bone mineral accretion across all puberty stages. However, additional factors contribute to bone modeling and remodeling. We showed that variation near genes that potentially contribute to mechanosensation may also modulate the response to physical activity. In addition, numerous endocrine pathways are necessary for bone mineral accrual, and during puberty, insulin-like growth factor 1 and gonadal steroids are required to promote normal bone accretion. Thus, the mechanical strain-related stimuli of height gain and physical activity are only a part of the complex cascade by which peak bone gain is achieved.
McCormack SE, Mitchell JA, Zemel BS. Adaptation of Bone to Mechanical Strain—Reply. JAMA Pediatr. 2018;172(2):196–197. doi:10.1001/jamapediatrics.2017.4654
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